1. Field of the Invention
The present invention relates to a planetary gear transmission wherein planetary gears are efficiently lubricated.
2. Discussion of the Prior Art
A power transmission incorporating a planetary gear mechanism is known. Such a planetary gear transmission is widely used for motor vehicles and industrial machines and equipment. In particular, the planetary gear transmission is most commonly used as an automatic transmission for motor vehicles, owing to its comparatively high degree of smoothness in changing the speed reduction ratio during power transmission, and its comparatively small size. Further, a planetary gear mechanism is used as an auxiliary transmission coupled to a continuously variable transmission, as disclosed in laid-open Publications Nos. 60-252857 and 61-130656.
In the planetary gear transmission incorporating a planetary gear mechanism, it is generally desirable to positively supply a lubricant to mutually meshing elements, bearings, and other element which are subject to loads while the transmission is operating to transmit power. In the planetary gear transmission for automotive vehicles, in particular, a smooth operation during power transmission requires a high level of gear meshing accuracy. That is, the planetary gears should maintain the required nominal or initial accuracy, and should be suitably supported with high precision for a prolonged period of service, so as to maintain the nominal meshing accuracy.
To achieve a positive lubrication of the planetary gear transmission as indicated above, a working fluid for operating the transmission is used as a lubricant. For instance, the working fluid returned into the housing of the transmission is pressurized by a hydraulic pump to produce a line pressure, and a portion of the pressurized fluid in the pressure line is fed as a lubricant to the meshing gears, bearings and other elements to be lubricated.
In the above arrangement wherein the working fluid pressurized by the hydraulic pump is used, a relatively large amount of the pressurized fluid in the pressure line is consumed for lubrication of the transmission. Consequently, an accordingly large portion of the power to drive the hydraulic pump is used for the lubrication. In the case where the transmission has a hydraulic actuator which is activated by the line pressure, the hydraulic pump must have a delivery capacity large enough to assure a normal functioning of the hydraulic actuator. Thus, the hydraulic pump requires a considerably large amount of drive power, and tends to be large-sized.